1 files changed, 30 insertions, 3 deletions

diff --git a/isa/checker.h b/isa/checker.h
index 6aae3ff..70393b6 100644
--- a/isa/checker.h
+++ b/isa/checker.h
@@ -1,19 +1,46 @@
 #pragma once
 
 #include <array>
+#include <map>
 
 #include "isa/isa.h"
 
 struct funcmem {
-    unsigned int fetch(unsigned int address);
-    void store(unsigned int address, unsigned int value);
+    static constexpr unsigned int PAGE_BYTES_LOG2 = 20;
+    static constexpr unsigned int PAGE_BYTES = 1 << PAGE_BYTES_LOG2;
+    static constexpr unsigned int PAGE_BYTE_OFFSET_MASK = PAGE_BYTES - 1;
+
+    typedef std::array<unsigned int, PAGE_BYTES> page;
+
+    std::map<unsigned int, page> image;
+
+    unsigned int fetch(unsigned int address) const {
+        auto page_address = address >> PAGE_BYTES_LOG2;
+        auto page_offset = address & PAGE_BYTE_OFFSET_MASK;
+        if (auto p = image.find(page_address); p != image.end()) {
+            const auto &page = p->second;
+            return page[page_offset];
+        }
+        return 0;
+    }
+
+    void store(unsigned int address, unsigned int value) {
+        auto page_address = address >> PAGE_BYTES_LOG2;
+        auto page_offset = address & PAGE_BYTE_OFFSET_MASK;
+        auto [p, emplaced] = image.try_emplace(page_address);
+        auto &page = p->second;
+        if (emplaced)
+            page.fill(0);
+        page[page_offset] = value;
+    }
 };
 
 struct checker {
     unsigned int acc = 0;
     unsigned int link = 0;
-    unsigned int pc = 0;
+    unsigned int pc = 00200;
     std::array<unsigned int, NUM_CTLREGS> ctlregs;
+    instruction_context inst;
     bool halted = false;
     funcmem mem;
     void execute();